Im building a coffee table that i wanted to have lights that would sync to the music i was playing or the games i would be playing. Did some research and found this was the best way to do (coffee table will be a later instructable).
Materials:
- 1 x TIP31 NPN Transistor - Radioshack # 276-2017
- 1 x 1/8" Audio Jack - Radioshack # 274-0249
- 1 x Toggle Switch (i used a covered one because i thought it looked cool, but any will work) - Radioshack # 275-601
- Roll of LED lights (or whatever you plan to use for lights) These are the cheapest i found and they included a power supply
http://www.amazon.com/gp/product/B00B0U9IAM/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1
- Breadboard

Here is video of them in action

Step 1: Build the Circuit

I built mine really small so i could fit it in the case but you could make it bigger so all the wires arent jammed together.
Cut a piece of breadboard to the size you want to build your circuit on.
You will also need to desolder the 12v end from the LED strip to be able to wire it into your circuit.
Wire two leads onto where you remove the 12v end from

Step 2: Wire Switch and Audio In

I used crimp on connectors so the switch could be taken out if needed but you could solder the wires on directly.
The audio is only wired in from one channel, i used the left channel but you could use the right. I eventually want to have two circuits set up and have different colored lights for each channel.

Step 3: Enclosure

I used the metal from an old floppy drive and just bent it into a little box
Draw out in marker where you want your holes and where you want the box bent at.
I used thinner metal so was able to cut with tin snips.
Drill the holes before you bend it into shape because depending on the thickness you are using it might just bend when you try to drill
You can paint the box now to make it look nice if you want to, i plan on doing this when i build my tv stand.
When you have the box all folded, place the switch and audio jack in there holes
You can then glue the circuit board into the case to have a clean look
I am waiting to glue the circuit board in until i have it mounted where i want it, this way i can drill screws into the top plate